Under Pressure (Kelly Lourcey)

Title: Under Pressure!

Principle(s) Investigated:

Bernoulli's Principle - an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid’s potential energy

Newton’s Laws of Motion - 1) An object at rest stays at rest, unless acted upon, 2) An object in motion stays in motion, unless acted upon (F = m*a), 3) For every action there is an equal and opposite reaction in nature.

Standards: MS-PS2-2 (PS2 Motion and Stability: Forces and Interactions) Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object.

Materials:

Textbook:

Pryer, K., Westleight, B.J., Greenwood, T., and Bainbridge-Smith. Physical Science for NGSS. Biozone Corporation. First Edition. Web <https://www.thebiozone.com/products/nps1/biozone-physical-sciences-for-ngss-student-edition/>

Part 1: Levitating Ball - ping pong ball and hair dryer

Part 2: Home-made Hovercraft - CD, bottle cap (collapsible), hot glue gun, and a balloon

Part 3: Paper Airplane - a single sheet of paper.

Procedure:

Part 1: Obtain a basic hair dryer. If possible, set the dryer temperature settings to low. Turn the hair dryer on to low and point it upward in a near vertical position. With your hand, place a ping pong ball in the pathway of the air being blown out of the hair dryer at a level that feels stable while still holding onto the ping pong ball. Once you feel stability for the ping pong ball, let go of it. The ping pong ball should remain in the stream of hair dryer air in a stable position. If you are able to, switch between high and low speed setting for the hair dryer to achieve the desired height for the ping pong ball to be above the hair dryer.

Part 2: Demonstrate by obtaining a CD (an old one I never anticipate using ever again), bottle cap (collapsible), hot glue gun with glue, and a balloon (large enough to fit over collapsible bottle cap). Assemble the materials such that the CD is the base and the cap is glued onto and over the center hole of the disk, as shown in Image 2a. Once the cap is secured against the CD, place the opening of the balloon over the bottle cap such that the lip of the balloon secures itself over and around the collapsible portion of the bottle cap, as shown in the smaller box of Image 2a. In order to inflate the balloon, set the bottle cap in the open position and blow up the balloon through the center of the CD, through the cap, and into the balloon. Set the bottle cap to a closed position once the desired amount of inflation is achieved. Place the bottom of the CD, with an inflated balloon, on a smooth surface. Open the bottle cap and let the hovercraft glide without friction along the smooth surface. There should be enough air flowing out of the balloon and under the hovercraft to cause it to lift off of the surface. At this point there is no friction between the smooth surface and the bottom of the hovercraft.

Part 3: Each student will obtain a single sheet of paper. The paper can be made of whatever material and have whatever pattern, as long as it is foldable and of a reasonable size. The student will then fold the paper into whatever airplane shape they think will work based on Part 1 and Part 2 (i.e. achieve maximum life and stability)

Student prior knowledge:

Students should have a basic understanding of pressure. Not only the phenomena of pressure, but also how it causes particles to move from regions of relatively high to relatively low pressures. Students should also have an understanding of scientific inquiry and the ability to form predictions and reflect on results from experimentation.

Explanation:

Lift:

In order for an aircraft to achieve lift it must overcome the force of gravity, as well as a balance of other forces like drage, weight, and thrust. The force providing lift must be at least equal to, if not greater than, the force of gravity on the mass of the aircraft (i.e. its weight). The thrust must also overcome the drag in order to sustain forward momentum. The wings and the belly of the aircraft are where the lift forces are applied. The component of lift for aircrafts is created by a pressure differential between the top and the bottom of its wings, which are tilted at various angles for maximum lift potential, refer to Figure 1. On top of the wings a low pressure system forms as a result of the majority of the air passing the wing is scooped and forced under the wing, this is where the high pressure system resides. Keeping in mind that the air around a flying aircraft is behaving like a fluid, and remembering Bernoulli's Principle, we can predict that the wings will begin to move upwards vertically due to the high pressure system under the wing pushing upwards towards the low pressure system. This is how lift is achieved. The components for lift can be calculated using Bernoulli’s equation (Eq 1) are the pressure (P), density of the air (⍴), and velocity of the aircraft (V).

P + ½⍴V2 = constant (Eq 1)

Bernoulli's Principle

In order for the ping pong ball to achieve lift, the forces confining it within the hair dryer’s stream of air are as a result of stabilized static pressure created from said stream of air. This stabilizing force is referred to as Bernoulli's Principle, which says that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid’s potential energy. Figure 2a and 2b showcase how the flow of air confines the ping pong ball using red to indicate higher pressure and blue indicating a lower pressure.

Part 1:

The hair dryer is blowing a focused column of air. The ping pong ball has a relatively small amount of mass which means the amount of air blowing out of a hair dryer should be sufficient to lift the ball. The ball is trapped due to high pressure systems forming all the way around the equatorial region of the ping pong ball. When the ping pong ball bounces from side to side, momentarily there are small low pressure systems that form on the side in which the ball is moving away from. This low pressure system causes the ball to move back towards the center where the low pressure system briefly developed. The ball also tends to bounce from side to side, always attempting to center itself within the column of air, the most stable position for the ping pong ball. Refer to Figure 2a and 2b, as well as this helpful demonstration video called Blow Dryer and Ping Pong Ball, and Figure 2c for a real world application of this phenomena.

Part 2:

The amount of air pressure trapped within the balloon should be enough to overcome the force of gravity holding the hovercraft to the surface it resides on, like a smooth table or tile floor. Once the balloon is blown up, the collapsible bottle cap is closed, and the craft is resting on a flat surface, the craft is ready to start hovering. The cap needs to be opened as wide and as fast as possible such that the air from within the balloon can rush out of the bottom and underneath the CD itself. The high pressure from within the balloon travels out and under the craft. The high pressure under the craft lifts it off of the surface by a very short distance (less than 1 cm), allowing it to glide and hover just above the surface. At this point, there is no friction between the craft and the surface it’s on. This is why hovercrafts glide across surfaces effortlessly. This lift is enough to counter the force of gravity acting on it, but any horizontal force will propel the craft without resistance due to the lack of friction.

Part 3:

Building paper airplanes at home allows students to experiment on an informal level. They have a chance to change their minds and designs based on trial and error. They should make at least 4 different plane shapes and adjustments, all with varying designs. The purpose of this is to cause the students to make focused choices and maintain a critical engineering mindset while improving their airplane designs.

Questions & Answers: Give three thought-provoking questions and p

Part 1: Levitating Ball

Q: What is keeping the ping pong ball from suddenly jumping out of the hair dryer’s column of air?

A: The ping pong ball is trapped in the hair dryer’s column of air because of high pressure systems that form on all sides. If the ping pong ball moves one way it will encounter the high pressure system surrounding it, pushing it back towards the center where the ping pong ball is more stable. Sometimes, however, the ping pong ball can over-correct itself bouncing slightly from one side to another, encountering the high pressure that surrounds it. It is perpetually redirected towards the center, appearing to bounce side-to-side.

Part 2: Home-made Hovercraft

Q: Is the CD with a balloon truly analogis to a hovercraft?

A: The ultimate answer is no, but for the most part the CD and balloon showcase the vertical component of a hovercraft, not the horizontal. All hovercrafts have a large fan in the rear. This fan also has rutters placed in the path of the fan’s air, allowing the pilot to steer it as it glides over whatever surface it’s traveling on. Refer to figure 3b for a diagram of a commercial hovercraft which showcases the vertical and horizontal components.

Part 3: Paper Airplane

Q: Do all aircrafts have to have a set of wings in order to achieve lift?

A: No, not all aircrafts have typical flat wings that project from either side of its center mass. There are a multitude of aircraft designs, all of which can be seen in the military, in modern commercial aircrafts, and homemade paper airplanes, some of which are listed below:

• Blended Wing Body - cross between conventional plan and a flying wing design that looks like a triangle in the sky.
• Semi-circular all-wing - compact design in which the wings were integrated into the body of the plane and appeared like a pancake in the sky.
• Flying Wing - a single long wing with a curve at the center that is the nose of the plane and appeared to look like a wedge flying through the sky.
• Boomerang - two bodied fuscelodge in which each side had a wing extending outward from it and attached by a smaller bit of wing between them.
• Ring Wing Glider - completely tubular shape with no mass at the center, but instead in the tube shape. The air passes through the center and the passengers and cargo reside in the circular fuscelodge.
• Straw & Circle Paper - Two Ring Wings with no tailing wing attached at similar points with a straw. The forward ring is slightly smaller than the tailing on.

Applications to Everyday Life:

Part 1: Bernoulli's Principles is applicable to a multitude of real-world applications. This principle is most widely used within the airline industry. However, there are other uses for this principle. In sports like baseball, a pitcher must guide a baseball into the strike zone of a batter with as much control over the ball as possible. The control is achieved by spinning the baseball when released from the pitcher’s hand and propelled towards home plate. The spinning action causes the air around the ball to move at a much faster speed than if it were to be thrown without a spin. The fast moving air generates a greater pressure differential between the air immediately surrounding the ball and the air it passes between the pitcher’s mound and home plate. The higher the pressure differential, the greater amount of force pushing the ball back into the path intended by the pitcher. Those pathways can be dictated by how the pitcher throws the ball, whether it has a back-spin, top-spin, curve ball, etc., depending on the direction of spin. The spin’s contribution to the directionality of the ball is called the Magnus Effect, illustrated in Figure 2c.

Part 2: The military is the largest entity that utilizes a similar system in which high pressure is pumped under a large vehicle, allowing it to maneuver and hover just over a relatively flat surface.

Part 3: The application of pressure is fundamental in the aircraft industry. Engineers design and build planes such that their wings provide sufficient lift while also minimizing drag reducing friction and other inefficiencies that may cost airline companies money. Their goal is to carry the maximum load from point A to point B while using the minimum amount of energy (i.e. jet fuel) to achieve it.

Photographs/GIFs: Include photos and diagrams that illustrate how the investigation is performed.

Lift:

Figure 1. This GIF shows normal airflow, an increased angle of attack, and a stall position for an aircraft’s wings. In a normal airflow position, there is no sign of lift, for the aerodynamics above and below the wing are the same. For the increased angle of attack, the wing is tilted with its underside facing the stream of air, leaving a disturbed pocket of air above and slightly behind the wing. In this position, lift is achieved due to the majority of the air being trapped under the wing, pushing it upwards into the low pressure pocket just above and behind it. In the stall position the angle of attack proves to be too steep, causing the aircraft to experience a stall. Too much of the high pressure air under the wing is flowing over and under the wing and not providing sufficient lift. (Multimedia Fluid Dynamics, Stanford University)

Part 1:

Figure 2a. This is a drawing of the demonstration shown in the video. As illustrated, the ping pong ball is trapped within the column of air coming from the hair dryer below. High pressure systems form on all sides of the ping pong ball, keeping it stable within the column of air. Of course, the velocity of the column of air holding the ping pong ball up is overcoming the force of gravity; but it is the high and low pressure systems that develop as a result of being trapped in said column of air that keeps the ball stable while in ‘flight.’

Figure 2b. This image showcases all of the forces keeping the ping pong ball in the hair dryer’s column of air. The force of gravity is overcome by the force of the air, which is the sum of the drag from the air itself and the friction of the ping pong balls outer texture. The colorful image to the right shows the velocity of air immediately surrounding the ping pong ball, and you can see high pressure systems forming, as indicated by the red, along the equatorial region and low pressure systems, as indicated by the blue, on the top and bottom. (Grüetzmacher, 2015)

Figure 2c. This diagram shows how the spin of a sports ball affects air flow around it. The top-spin portion shows a high pressure system forming above the ball and low pressure system just below, meaning ‘lift’ forces are being applied in a downward direction. The back-spin is opposite of this, forming high pressure systems on the bottom and low pressure systems on the top causes lift forces to act on the underside of the ball pushing upwards against gravity. (tennis.warehouse.com)

Part 2:

Figure 3a. This is a drawing of how the home-made hovercraft should look in action. The cap glued to the CD and covered by the mouth of the inflated balloon is open allowing the air inside the balloon to escape. Not only does it allow the air to escape, but allows the high pressure air inside the balloon to escape quickly, pushing air out of the balloon and under the CD base. When the pressure inside the balloon is greater than the combined weight of the home-made hovercraft, it will rise and no longer be touching the surface it was previously resting on. Once the hovercraft has achieved lift, it can move and glide horizontally anywhere with no friction to slow its movement.

Figure 3b. This is a diagram above depicts a hovercraft large enough to carry passengers and cargo. Lift is indicated by the red arrows placed in a vertical position and are pointed in the up direction. The blue arrows indicate air movement in the horizontal direction. Most of the blue arrows are located nearest the large fan at the rear-end of the hovercraft. This fan provides horizontal thrust. Thrust pointed downward is responsible for providing lift.

Part 3:

Figure 4. This is an illustration of a paper airplane in flight and passing through air. The flow of air is indicated by the lines approaching the aircraft from the front and subsequently splitting and either going over or under the wings. The blue indicates the air going over the wings, eventually being used to form low pressures systems; and the red indicating the air going under the wings and eventually being used in high pressures systems. Because a paper airplane aircraft is lightweight, the pressure differential between the top and the bottom of the aircraft is small.

Videos: Find my video by clicking on ScienceInvestigation Lourcey SP 2020. I’ve also generated an EdPuzzle for the same video.

References

1. Gruetzmacher, Mike. Geek Hub. Engineering Edge. Mechanical analysis. Mentor - A Siemens Business. Search Mentor.com. Web. Vol 4, Issue 2. 2015. <https://www.mentor.com/products/mechanical/engineering-edge/volume4/issue2/geek-hub>
2. 13.021 - Marine Hydrodynamics. Lecture 24C - Lifting Surfaces. Multimedia fluid mechanics. Stanford University. Web <http://web.mit.edu/13.021/13021_2003/Lifting%20surfaces/lectureC.htm>
3. Theory of Flight. MIT Department of Aeronautics and Astronautics. Man-Vehicle Laboratory.16 march 1997. Web <https://web.mit.edu/16.00/www/aec/flight.html>
4. How does a Hovercraft work?. Amphibious Marine Hovercraft for Business & Adventure. Hovercraft Manufacturing and Sales. 2020. Web <https://www.amphibiousmarine.com/how-does-a-hovercraft-work/>